A pressure sensor having a sensing unit and a pressure transmitting rod both housed in a case is proposed in JP-A-5-34241. The sensing unit, such as a strain gage, outputs signals according to pressure levels. The case has a pipe portion that extends from a sensing unit housing portion and an opening at an end of the pipe portion. A pressure receiving diaphragm is fixed to the end of the pipe portion by welding such that it covers the opening. The pressure transmitting rod is arranged such that its first end and second end are located on the sensing unit side and the pressure receiving diaphragm side, respectively. Pressure applied to the pressure receiving diaphragm is transmitted to the sensing unit via the pressure transmitting rod.
The pressure sensor is fixed to a subject, such as an engine block, by inserting the pipe portion into a mounting hole provided in the subject until the end of the pipe portion touches an inner surface of the subject via the diaphragm. The opening of the pipe portion is sealed with the diaphragm. The contact between the pipe portion and the inner surface of the subject creates stress, namely, a force is applied to the pipe portion in its longitudinal direction and the pipe portion is pushed toward the sensing unit. The stress is also applied to the pressure transmitting rod. As a result, the pressure transmitting rod is pressed against the sensing unit and an abnormal signal is outputted from the pressure sensor.